1. Field of the Invention
The present invention relates to systems for monitoring chemical processes. In particular, the present invention relates to fiber optic-based systems for monitoring in-line the concentrations of substances used in chemical processes.
2. Discussion of Background
Absorption spectrophotometry is one of the techniques which has long been recognized as adaptable for on-line chemical analysis. The technique is simple, relatively easy to interface with industrial and laboratory chemical processes, and can be selective and sensitive for analytes which absorb light.
Commercially available filter photometry devices provide reliable high-precision on-line data. These systems typically monitor two optical frequencies, one coincident with analyte absorption and the other at a point of no absorption. These devices automatically account for spectral baseline shifts, but are severely affected by interfering chromophores as well as changes in analyte absorptivity due to varying matrix conditions. More sophisticated spectrophotometric measurement devices which collect multiple channels of data can correct for some of these effects but, until recently, have been too complicated and delicate for process environments.
At the Savannah River Plant, several commercial two-wavelength filter photometers have been modified with fiber optic cables to monitor the elusion of neptunium and plutonium from anion exchange columns. Researchers at Oak Ridge National Laboratory developed a fiber optic photometer based on a rotating filter wheel to monitor the concentration of uranium and plutonium in process streams. Workers in France have developed similar analyzers using industrial photometers with as many as five measurement wavelengths. A multiplexed concentration analyzer has also been developed by the French using optical fibers and a commercial diode array spectrophotometer. This analyzer can monitor up to four sample locations in series acquiring data over the 400-800 nanometer range.
However, there remains a need for an on-line, fiber-optic-based apparatus for accurate, validated monitoring of chemical concentrations, an apparatus easily deployable at a large number of locations throughout a system and capable of rapid data acquisition and reduction.